`yii\web\User::loginRequired()` now returns the `Response` object instead of exiting the application

Fixes #802: Added support for retrieving sub-array element or child object property through `ArrayHelper::getValue()`

After ensureBehaviors() call $this->_behaviors is an array already.
And since detachBehavior() unsets elements in $this->_behaviors, $this->_behaviors turns out to be an empty array after all iterations.

Fixes #1586: `QueryBuilder::buildLikeCondition()` will now escape special characters and use percentage characters by default

Fixes #1681: Added support for automatically adjusting the "for" attribute of label generated by `ActiveField::label()`